Variable length fixation device

Abstract

A variable length fixation device for insertion into a hole formed in two or more bone fragments has a barrel portion and a fastener element. The barrel portion is secured to an inside surface of the hole in a proximal one of the bone fragments. The fastener element is telescopically mounted to the barrel portion and is extendable into a distal one of the bone fragments. The assembly prevents lateral movements of the distal fragment, relative to the proximal fragment, while allowing axial relative movements (i.e., linear movements along the longitudinal axis of the fastener element) to occur. In a preferred embodiment, the fastener element is a cannulated bone screw having a hex-shaped cross-section on one end which is telescopically received into a hex-shaped interior of the hollow barrel portion. The two components are preferably permanently joined to form a one-piece assembly having a variable overall length. The fixation device of the present invention is substantially insertable in its entirety into the hole which extends across the fracture site, and may be installed with a minimal amount of trauma and damage to surrounding bone and soft tissues.

What is claimed is: 
     
       1. A screw for fixing proximal and distal fragments in a bone fracture, comprising (A) a first and second element that (1) are non-separably interconnected,   (2) each have a longitudinal axis in line with the other,   (3) longitudinally telescope with each other, and   (4) have means for rotationally fixing the elements to each other;     (B) the first element having (1) a first shank portion, and   (2) screw threads at one end of the first shank portion integral therewith for engaging the distal fragment;     (C) the second element having (1) a second shank portion in the form of a sleeve, free of threads on its outer surface for engaging the proximal fragment that longitudinally, slidably fits over the first shank portion of the first element, and   (2) a head at an end of the second shank portion remote from the screw threads on the first shank portion for receiving means for turning the screw.     
     
     
       2. A screw of claim 1 having means for retaining the second element in the proximal fragment. 
     
     
       3. The screw of claim 2 wherein the means for retaining the second element in the proximal fragment comprise a plurality of locking rings formed on the outer surface of the second element. 
     
     
       4. A screw of claim 1 wherein the means for rotationally fixing the elements to each other comprise a hexagonally-shaped outer surface on the first shank portion, and a hexagonally-shaped inner surface in the second shank portion. 
     
     
       5. A screw of claim 1 wherein the head of the second element has a hexagonally-shaped recess to receive wrench means for turning the screw. 
     
     
       6. A screw of claim 1 wherein the first and second element are hollow and are adapted for insertion over a guide pin positioned in the proximal and distal fragments.